Laboratory Findings and Biomarkers in Long COVID: What Do We Know So Far? Insights into Epidemiology, Pathogenesis, Therapeutic Perspectives and Challenges

The Power of Antibodies: Advancing Biomarker-Based Disease Detection and Surveillance

BACKGROUND

Antibodies have long served as fundamental tools in disease diagnosis and surveillance. Their utility as biomarkers has expanded beyond infectious diseases to encompass a wide range of health conditions.

OBJECTIVES

This review aims to explore recent advancements in antibody biomarker discovery and their applications in diagnosing and monitoring diverse health conditions. It also examines the role of antibody surveillance in public health and epidemiological studies.

METHODS

A comprehensive analysis of recent literature was conducted, focusing on studies that identify and characterize disease-specific antibodies. Particular attention was given to their relevance in autoimmune diseases, infections, cancers, and neurological disorders.

CONTENT

The review highlights disease-specific antibody biomarkers and their clinical significance. It also discusses the utility and challenges of antibody-based surveillance in assessing disease prevalence, tracking immunity trends, and supporting One Health strategies.

CONCLUSIONS

Recent advancements in antibody biomarker discovery demonstrate significant potential in improving early diagnosis, personalized treatment, and population-level health management. Antibody surveillance continues to play a pivotal role in guiding public health responses and understanding disease dynamics.

ORCHESTRA Delphi consensus: diagnostic and therapeutic management of Post-COVID-19 condition in vulnerable populations

BACKGROUND

Post-COVID condition (PCC) remains poorly understood, especially in clinically vulnerable groups. Within the ORCHESTRA Project, we applied the Delphi approach to drive recommendations for the diagnosis, management, and prevention of PCC in people living with HIV (PWH) and patients affected by rheumatological diseases (RD) and haematological malignancies (HM).

METHODS

Based on literature review, three areas of interest in PCC in PWH, HM, and RD were identified: 1) features and risk factors; 2) diagnosis and management; and 3) prevention. A three-round Delphi anonymous survey consisting of 15 questions was conducted including 69 experts. Consensus was measured by the 6-point Likert scale categorised into four tiers: strong disagreement, moderate disagreement, moderate agreement, and strong agreement. Statements were generated on questions achieving consensus.

RESULTS

Eleven statements were generated: six on features and risk factors of PCC in clinically vulnerable populations, two on diagnosis and management, and three on prevention. Chronic fatigue was identified as the most frequent presentation of PCC in PWH and RD populations. A different case definition of PCC is required for RD population, as symptoms of PCC and autoimmune disorders may overlap. Risk factors for PCC include age>65, severity of COVID-19, and female sex; this latter is also associated with increased smell/taste impairment. A clinical assessment or a routine laboratory test performed three months after acute infection is not suggested to diagnose PCC in PWH. PWH and RD should be screened to exclude additional autoimmune disorders in case of chronic fatigue/arthralgia of new onset. Full-course vaccination and early treatment for COVID-19 should be promoted to prevent PCC, while corticosteroids during acute infection are not recommended.

CONCLUSION

Diagnosis, management and prevention of PCC are still under discussion. This Delphi offers valuable insights on PCC in selected clinically vulnerable populations and suggests a tailored approach in vulnerable populations.

Early biomarkers in hospitalized patients as predictors of post-acute sequelae of SARS-CoV-2 infection: a one-year cohort study

BACKGROUND

Post-acute sequelae of SARS-CoV-2 infection (PASC) represent a significant challenge in patient care, with symptoms persisting beyond three month's post-recovery. This study aimed to evaluate the incidence of PASC at one year post-COVID-19 and identify predictive biomarkers and comorbidities for effective risk stratification.

METHODS

A cohort of 120 adult patients, including 50 intensive care and 70 non-intensive care patients, was followed up at two weeks, six weeks, and one-year post-discharge using structured questionnaires. The study integrated comorbidities and laboratory biomarkers to forecast the risk for PASC.

RESULTS

The median age of participants was 56 years, with 40% having moderate to severe comorbidities. A year post-recovery, 32.8% exhibited post COVID-19 conditions. The most common symptoms were constitutional (16%), respiratory (8.4%), and neuropsychiatric (2.5%). Bayesian network analysis indicated significant correlations between constitutional symptoms, rehospitalisation, and biomarkers including C-reactive protein, lactate-dehydrogenase, ferritin, and albumin.

CONCLUSION

This study highlights the prolonged impact of PASC, one-year post infection. It highlights the role of specific biomarkers such as C-reactive protein, lactate-dehydrogenase, ferritin, and albumin in tailoring individual patient care by advancing understanding in post-COVID-19 symptoms prediction. Our findings support the need for further research to refine these insights, which are pivotal for the ongoing care of patients in the aftermath of COVID-19.

Interrelationships Between Plasma Levels of Brain Natriuretic Peptide and Prolonged Symptoms Due to Long COVID

Objectives: Evidence for the usefulness of biomarkers that aid in diagnosis, assessment of severity, and prediction of prognosis in patients with long COVID is limited. The aim of this study was to clarify the characteristics of brain natriuretic peptide (BNP) in long COVID. Methods: We conducted a retrospective observational study of patients who visited the COVID-19 aftercare outpatient clinic at Okayama University Hospital from February 2021 to April 2024. Results: A total of 428 patients were enrolled in this study, and the patients were divided into a group with normal BNP (n = 314, ≤18.4 pg/mL) and a group with increased BNP (n = 114, >18.4 pg/mL). The long COVID group with increased BNP had a higher proportion of females (44.3% vs. 73.7%, p < 0.01) and an older median age (38 vs. 51 years, p < 0.01). Fatigue and brain fog were commonly manifested in both groups, while dyspnea was a more frequent complaint in the group with increased BNP. Various symptoms including fatigue, palpitations, and taste and/or olfactory disorders were associated with elevated BNP (23 to 24 pg/mL). Memory impairment was also linked to higher BNP (OR: 2.36, p = 0.05). In long COVID patients, plasma BNP elevation appears to be more pronounced in females and is often related to cardiogenic factors, in which inflammatory responses are also involved. Conclusions: Plasma BNP measurement may be useful for evaluating the severity of long COVID, especially in female patients and those with respiratory symptoms and/or memory impairment.

Chronic inflammation in post-acute sequelae of COVID-19 modulates gut microbiome: a review of literature on COVID-19 sequelae and gut dysbiosis

BACKGROUND

Long COVID or Post-acute sequelae of COVID-19 is an emerging syndrome, recognized in COVID-19 patients who suffer from mild to severe illness and do not recover completely. Most studies define Long COVID, through symptoms like fatigue, brain fog, joint pain, and headache prevailing four or more weeks post-initial infection. Global variations in Long COVID presentation and symptoms make it challenging to standardize features of Long COVID. Long COVID appears to be accompanied by an auto-immune multi-faceted syndrome where the virus or viral antigen persistence causes continuous stimulation of the immune response, resulting in multi-organ immune dysregulation.

MAIN TEXT

This review is focused on understanding the risk factors of Long COVID with a special emphasis on the dysregulation of the gut-brain axis. Two proposed mechanisms are discussed here. The first mechanism is related to the dysfunction of angiotensin-converting enzyme 2 receptor due to Severe Acute Respiratory Syndrome Corona Virus 2 infection, leading to impaired mTOR pathway activation, reduced AMP secretion, and causing dysbiotic changes in the gut. Secondly, gut-brain axis dysregulation accompanied by decreased production of short-chain fatty acids, impaired enteroendocrine cell function, and increased leakiness of the gut, which favors translocation of pathogens or lipopolysaccharide in circulation causing the release of pro-inflammatory cytokines. The altered Hypothalamic-Pituitary-Adrenal axis is accompanied by the reduced level of neurotransmitter, and decreased stimulation of the vagus nerve, which may cause neuroinflammation and dysregulation of serum cortisol levels. The dysbiotic microbiome in Long COVID patients is characterized by a decrease in beneficial short chain fatty acid-producing bacteria (Faecalibacterium, Ruminococcus, Dorea, and Bifidobacterium) and an increase in opportunistic bacteria (Corynebacterium, Streptococcus, Enterococcus). This dysbiosis is transient and may be impacted by interventions including probiotics, and dietary supplements.

CONCLUSIONS

Further studies are required to understand the geographic variation, racial and ethnic differences in phenotypes of Long COVID, the influence of viral strains on existing and emerging phenotypes, to explore long-term effects of gut dysbiosis, and gut-brain axis dysregulation, as well as the potential role of diet and probiotics in alleviating those symptoms.

Treatment with Sulodexide Downregulates Biomarkers for Endothelial Dysfunction in Convalescent COVID-19 Patients

INTRODUCTION

Persistent elevation of biomarkers associated with endothelial dysfunction in convalescent COVID-19 patients has been linked to an increased risk of long-term cardiovascular complications, including long COVID syndrome. Sulodexide, known for its vascular endothelial affinity, has demonstrated pleiotropic protective properties. This study aims to evaluate the impact of sulodexide on serum levels of endothelial dysfunction biomarkers in patients during the convalescent phase of COVID-19.

METHODS

We conducted a double-blind, single-center, randomized, placebo-controlled trial in Mexico, comparing sulodexide (250 LRU orally, twice daily) with placebo over 8 weeks in adult patients during early COVID-19 convalescence. Differences in serum biomarkers between the groups were analyzed using repeated measures and post hoc tests, with Thrombomodulin (TM) as the primary endpoint.

RESULTS

Among 206 analyzed patients (103 in each group), at week 8, the sulodexide group exhibited significantly lower mean levels of Thrombomodulin (TM) (25.2 ± 7.9 ng/mL vs 29.9 ± 14.7 ng/mL, P = .03), von Willebrand Factor (vWF) (232 ± 131 U/dL vs 266 ± 122 U/dL, P = .02) and Interleukin-6 (IL-6) (12.5 ± 13.2 pg/mL vs 16.2 ± 16.5 pg/mL, P = .03) compared to the placebo group. D-dimer and C reactive protein (CRP) in the sulodexide group were also lowered. No significant differences were observed for P-selectin, fibrinogen, VCAM-1, or ICAM-1 levels.

CONCLUSIONS

Patients in the convalescent phase of COVID-19 who received sulodexide for eight weeks showed a reduction in TM, vWF, D-dimer, CRP, and IL-6 serum levels compared to placebo. These findings suggest a potential protective effect of sulodexide against thromboinflammation and endothelial damage.

Post-COVID-19 Condition and Pulmonary Embolism

Purpose

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes post-acute sequelae of coronavirus disease 2019 (COVID-19), including pulmonary vasculopathy, increasing thrombotic risk. Screening and treating survivors are essential to reduce associated disabilities. We aim to investigate the clinical characteristics of patients with post-COVID-19 condition and pulmonary embolism, as well as their health-related quality of life one year after COVID-19 diagnosis.

Patients and Methods

In our study, we analyzed nine cases of post-COVID-19 condition and pulmonary embolism in a tertiary hospital in Taiwan. Patient characteristics, including age, sex, symptoms, and outcomes, were recorded. One year post-diagnosis, patients underwent follow-up with lab tests, chest X-rays, electrocardiograms, and health-related quality of life (HRQOL) assessments using the EuroQoL 5-Dimension 5-Level (EQ-5D-5L) tool.

Results

Post-COVID-19 condition with pulmonary embolism predominantly affects females. Common symptoms include breathlessness and chest pain, and a lung perfusion scan may be useful for diagnosis. The one-year follow-up of five patients mainly showed normal lab results and no active lung lesions. The mean EQ-5D score was 0.928 ± 0.119, and the EQ visual analogue scale (EQ-VAS) was 85.00 ± 11.18. Pain/discomfort was the most reported issue.

Conclusion

This research reveals that post-COVID-19 condition with pulmonary embolism affects a significant number of women and those with preexisting conditions like cancer or diabetes. Symptoms overlap also complicates diagnosis. Although many lab results were normal, the elevated risk of pulmonary embolism persists. Lower utility scores and increased anxiety highlight the need for targeted interventions and mental health support. Our study underscores the importance of monitoring pulmonary embolism in patients after COVID-19 infection, given the significant impact on post-COVID-19 condition and overall health outcomes.

Trends of common laboratory biomarkers after SARS-CoV-2 infection

BACKGROUND

Most studies that explore the long-term effects of COVID-19 are based on subjectively reported symptoms, while laboratory-measured biomarkers are mainly examined in studies of relatively small cohorts. This study investigates the long-term effects of SARS-CoV-2 infection on common laboratory biomarkers.

METHODS

We utilized a retrospective cohort of SARS-CoV-2 infected individuals and rigorously matched controls based on demographic and clinical characteristics, examining 63 common laboratory biomarkers. Additional lab-specific cohorts were matched with an additional criterion of baseline biomarker values. Differences in biomarkers over a 12-month follow-up were analyzed using standardized mean difference-in-differences.

RESULTS

The general cohort included 361,061 matched pairs, with 26M laboratory results. The effects on most biomarkers lasted 1-4 months and were consistent with anticipated changes after acute viral infections. Some biomarkers presented prolonged effects, consistent across the general and lab-specific cohorts. One group of such findings included a 7-8 month decrease in WBC counts, mainly driven by decreased counts of neutrophils, monocytes, and basophils. Potassium levels were decreased for 3-5 months. Vaccinated individuals' data suggested potentially smaller effects on WBCs, but cohort sizes limited this analysis.

CONCLUSIONS

This study explores SARS-CoV-2 infection effects on common laboratory biomarkers, characterizing the direction and duration of these effects on the largest infected cohort to date. The effects of most biomarkers resolve in the first months following infection. The most notable longer-lasting effects involved the immune system. Further research is required to characterize the magnitude of these effects among specific individuals.

A Single-Center Pilot Study of Therapeutic Apheresis in Patients with Severe Post-COVID Syndrome

After the COVID-19 pandemic, many patients have reported chronic fatigue and severe post-exertional malaise, with symptoms similar to those of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The accumulation of agonistic receptor autoantibodies targeting beta-adrenergic (β1 and β2) and muscarinic (M3 and M4) neurotransmitter receptors may play a crucial role in the pathomechanism of both ME/CFS and post-COVID conditions. Therapeutic apheresis has been suggested as an effective treatment option for alleviating and mitigating symptoms in this desperate group of patients. In this single-center pilot study, we analyzed autoantibodies in a cohort of 20 post-COVID patients before and after therapeutic apheresis. Apheresis resulted in a decline of β1 or β2 adrenergic receptor antibodies in all patients. Additionally, the majority of patients experienced a concurrent reduction in symptoms such as fatigue, physical activity restrictions, myalgia, post-exertional malaise, and concentration disorders. This study clearly demonstrates an association between autoantibodies and the clinical improvement of post-COVID patients. Even if future sham-controlled trials do not show a positive outcome, extracorporeal apheresis may still be valuable for this patient group by temporarily improving microperfusion and symptoms. Success in restoring patients to work and normal life, as observed in many individuals after therapeutic apheresis, should be recognized. Therefore, we believe that extracorporeal therapeutic apheresis, as part of a multimodal treatment, should be considered an early intervention for postinfectious syndromes in selected patients.

Exploring metabolic anomalies in COVID-19 and post-COVID-19: a machine learning approach with explainable artificial intelligence

The COVID-19 pandemic, caused by SARS-CoV-2, has led to significant challenges worldwide, including diverse clinical outcomes and prolonged post-recovery symptoms known as Long COVID or Post-COVID-19 syndrome. Emerging evidence suggests a crucial role of metabolic reprogramming in the infection's long-term consequences. This study employs a novel approach utilizing machine learning (ML) and explainable artificial intelligence (XAI) to analyze metabolic alterations in COVID-19 and Post-COVID-19 patients. Samples were taken from a cohort of 142 COVID-19, 48 Post-COVID-19, and 38 control patients, comprising 111 identified metabolites. Traditional analysis methods, like PCA and PLS-DA, were compared with ML techniques, particularly eXtreme Gradient Boosting (XGBoost) enhanced by SHAP (SHapley Additive exPlanations) values for explainability. XGBoost, combined with SHAP, outperformed traditional methods, demonstrating superior predictive performance and providing new insights into the metabolic basis of the disease's progression and aftermath. The analysis revealed metabolomic subgroups within the COVID-19 and Post-COVID-19 conditions, suggesting heterogeneous metabolic responses to the infection and its long-term impacts. Key metabolic signatures in Post-COVID-19 include taurine, glutamine, alpha-Ketoglutaric acid, and LysoPC a C16:0. This study highlights the potential of integrating ML and XAI for a fine-grained description in metabolomics research, offering a more detailed understanding of metabolic anomalies in COVID-19 and Post-COVID-19 conditions.

Differentiation of Prior SARS-CoV-2 Infection and Postacute Sequelae by Standard Clinical Laboratory Measurements in the RECOVER Cohort

BACKGROUND

There are currently no validated clinical biomarkers of postacute sequelae of SARS-CoV-2 infection (PASC).

OBJECTIVE

To investigate clinical laboratory markers of SARS-CoV-2 and PASC.

DESIGN

Propensity score-weighted linear regression models were fitted to evaluate differences in mean laboratory measures by prior infection and PASC index (≥12 vs. 0). (ClinicalTrials.gov: NCT05172024).

SETTING

83 enrolling sites.

PARTICIPANTS

RECOVER-Adult cohort participants with or without SARS-CoV-2 infection with a study visit and laboratory measures 6 months after the index date (or at enrollment if >6 months after the index date). Participants were excluded if the 6-month visit occurred within 30 days of reinfection.

MEASUREMENTS

Participants completed questionnaires and standard clinical laboratory tests.

RESULTS

Among 10 094 participants, 8746 had prior SARS-CoV-2 infection, 1348 were uninfected, 1880 had a PASC index of 12 or higher, and 3351 had a PASC index of zero. After propensity score adjustment, participants with prior infection had a lower mean platelet count (265.9 × 109 cells/L [95% CI, 264.5 to 267.4 × 109 cells/L]) than participants without known prior infection (275.2 × 109 cells/L [CI, 268.5 to 282.0 × 109 cells/L]), as well as higher mean hemoglobin A1c (HbA1c) level (5.58% [CI, 5.56% to 5.60%] vs. 5.46% [CI, 5.40% to 5.51%]) and urinary albumin-creatinine ratio (81.9 mg/g [CI, 67.5 to 96.2 mg/g] vs. 43.0 mg/g [CI, 25.4 to 60.6 mg/g]), although differences were of modest clinical significance. The difference in HbA1c levels was attenuated after participants with preexisting diabetes were excluded. Among participants with prior infection, no meaningful differences in mean laboratory values were found between those with a PASC index of 12 or higher and those with a PASC index of zero.

LIMITATION

Whether differences in laboratory markers represent consequences of or risk factors for SARS-CoV-2 infection could not be determined.

CONCLUSION

Overall, no evidence was found that any of the 25 routine clinical laboratory values assessed in this study could serve as a clinically useful biomarker of PASC.

PRIMARY FUNDING SOURCE

National Institutes of Health.

Laboratory profiling of patients with long COVID in the Brazilian Amazon region: A cross-sectional study

The condition commonly referred to as long coronavirus disease (COVID) is characterized by the continuation of symptoms, sometimes accompanied by new symptoms that persist after the resolution of acute coronavirus disease 2019 (COVID-19). This observational cross-sectional study investigated 332 patients with long COVID in the Brazilian Amazon region. The study aimed to elucidate the systemic interactions associated with long COVID by compiling the findings related to hematological, coagulation, immunological, metabolic, hepatic, renal, and muscular profiles. Participants with long COVID were identified using rigorous criteria and underwent thorough laboratory examinations. The obtained data were subsequently analyzed, allowing for comparisons, associations, and correlations between findings within distinct groups in the study. Significant associations were observed between hospitalization during the acute phase and persistent laboratory abnormalities, suggesting a potential link between acute severity and long-term effects. Notably, individuals with long COVID for over a year exhibited elevated levels of monocytes, prolonged prothrombin times, reduced prothrombin activity, high levels of lactate dehydrogenase, and an increased frequency of qualitative C-reactive protein detection. This study provides valuable insights into the laboratory risk profile of patients with long COVID, particularly in the unique context of the Amazon region, where patients exhibit persistent symptoms lasting up to 1261 days.

Diaphragmatic strengthening exercises for patients with post COVID-19 condition after mild-to-moderate acute COVID-19 infection: a randomized controlled study

OBJECTIVE

To assess the clinical effects of incentive spirometry (IS) and diaphragmatic breathing (DB) in patients with post COVID-19 condition and diaphragmatic dysfunction as compared with the standard care alone.

METHODS

The present longitudinal randomized study included 60 patients with post COVID-19 condition and diaphragmatic dysfunction. Patients were equally randomized to receive standard care plus IS (G1), standard care plus DB (G2) or standard care alone (G3) for 8 weeks. The primary outcome is clinical improvement as evaluated by the modified Medical Research Council (mMRC) dyspnoea scale.

RESULTS

Comparison between the studied groups revealed significant improvement in G1 and G2 in all parameters at the end of follow-up. However, no significant improvement was found in G3. At the end of follow-up, 15 patients (75.0%) in G1, 11 patients (55.0%) in G2, and 3 patients (15.0%) in G3 showed improvement on the mMRC dyspnoea scale. Multivariate logistic regression analysis identified mild acute COVID-19 infection (p = 0.009), use of IS (p < 0.001), and use of DB (p = 0.023) as significant predictors of improvement on the mMRC dyspnoea scale.

CONCLUSIONS

IS or DB training in addition to the standard care in post COVID-19 condition was associated with better clinical improvement as compared with the standard care alone.

Navigating the Long Haul: A Comprehensive Review of Long-COVID Sequelae, Patient Impact, Pathogenesis, and Management

Long COVID, characterized by persistent symptoms following a SARS-CoV-2 infection, presents a significant public health challenge with wide-ranging implications. This comprehensive review explores the epidemiology, clinical manifestations, pathogenesis, risk factors, diagnosis, patient impact, management strategies, and long-term prognosis of COVID. Despite a varied symptomatology that spans multiple organ systems, including respiratory, neurological, and cardiovascular systems, this condition is primarily associated with chronic inflammation and potential viral persistence. Prevalence varies, influenced by the initial infection severity, demographic factors, and pre-existing conditions. The review emphasizes the necessity for healthcare systems to adapt to the needs of long-COVID patients by developing standardized diagnostic criteria and personalized, multidisciplinary treatment approaches. Current research gaps and future directions are identified, highlighting the urgent need for further studies on pathophysiological mechanisms and effective therapeutic interventions. This review aims to inform healthcare providers, researchers, and policymakers, enhancing patient care and guiding ongoing and future research initiatives. The continuing global focus and collaborative efforts offer hope for improved outcomes for those affected by long COVID, marking an essential step towards addressing this emergent condition comprehensively.

Association of circulating biomarkers with illness severity measures differentiates myalgic encephalomyelitis/chronic fatigue syndrome and post-COVID-19 condition: a prospective pilot cohort study

BACKGROUND

Accumulating evidence suggests that autonomic dysfunction and persistent systemic inflammation are common clinical features in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID. However, there is limited knowledge regarding their potential association with circulating biomarkers and illness severity in these conditions.

METHODS

This single-site, prospective, cross-sectional, pilot cohort study aimed to distinguish between the two patient populations by using self-reported outcome measures and circulating biomarkers of endothelial function and systemic inflammation status. Thirty-one individuals with ME/CFS, 23 individuals with long COVID, and 31 matched sedentary healthy controls were included. All study participants underwent non-invasive cardiovascular hemodynamic challenge testing (10 min NASA lean test) for assessment of orthostatic intolerance. Regression analysis was used to examine associations between outcome measures and circulating biomarkers in the study participants. Classification across groups was based on principal component and discriminant analyses.

RESULTS

Four ME/CFS patients (13%), 1 with long COVID (4%), and 1 healthy control (3%) presented postural orthostatic tachycardia syndrome (POTS) using the 10-min NASA lean test. Compared with matched healthy controls, ME/CFS and long COVID subjects showed higher levels of ET-1 (p < 0.05) and VCAM-1 (p < 0.001), and lower levels of nitrites (NOx assessed as NO2- + NO3-) (p < 0.01). ME/CFS patients also showed higher levels of serpin E1 (PAI-1) and E-selectin than did both long COVID and matched control subjects (p < 0.01 in all cases). Long COVID patients had lower TSP-1 levels than did ME/CFS patients and matched sedentary healthy controls (p < 0.001). As for inflammation biomarkers, both long COVID and ME/CFS subjects had higher levels of TNF-α than did matched healthy controls (p < 0.01 in both comparisons). Compared with controls, ME/CFS patients had higher levels of IL-1β (p < 0.001), IL-4 (p < 0.001), IL-6 (p < 0.01), IL-10 (p < 0.001), IP-10 (p < 0.05), and leptin (p < 0.001). Principal component analysis supported differentiation between groups based on self-reported outcome measures and biomarkers of endothelial function and inflammatory status in the study population.

CONCLUSIONS

Our findings revealed that combining biomarkers of endothelial dysfunction and inflammation with outcome measures differentiate ME/CFS and Long COVID using robust discriminant analysis of principal components. Further research is needed to provide a more comprehensive characterization of these underlying pathomechanisms, which could be promising targets for therapeutic and preventive strategies in these conditions.

Post-COVID dysautonomias: what we know and (mainly) what we don't know

Following on from the COVID-19 pandemic is another worldwide public health challenge that is referred to variously as long COVID, post-COVID syndrome or post-acute sequelae of SARS-CoV-2 infection (PASC). PASC comes in many forms and affects all body organs. This heterogeneous presentation suggests involvement of the autonomic nervous system (ANS), which has numerous roles in the maintenance of homeostasis and coordination of responses to various stressors. Thus far, studies of ANS dysregulation in people with PASC have been largely observational and descriptive, based on symptom inventories or objective but indirect measures of cardiovascular function, and have paid little attention to the adrenomedullary, hormonal and enteric nervous components of the ANS. Such investigations do not consider the syndromic nature of autonomic dysfunction. This Review provides an update on the literature relating to ANS abnormalities in people with post-COVID syndrome and presents a theoretical perspective on how the ANS might participate in common features of PASC.

Traumatic Brain Injury in the Long-COVID Era

Major determinants of the biological background or reserve, such as age, biological sex, comorbidities (diabetes, hypertension, obesity, etc.), and medications (e.g., anticoagulants), are known to affect outcome after traumatic brain injury (TBI). With the unparalleled data richness of coronavirus disease 2019 (COVID-19; ∼375,000 and counting!) as well as the chronic form, long-COVID, also called post-acute sequelae SARS-CoV-2 infection (PASC), publications (∼30,000 and counting) covering virtually every aspect of the diseases, pathomechanisms, biomarkers, disease phases, symptomatology, etc., have provided a unique opportunity to better understand and appreciate the holistic nature of diseases, interconnectivity between organ systems, and importance of biological background in modifying disease trajectories and affecting outcomes. Such a holistic approach is badly needed to better understand TBI-induced conditions in their totality. Here, I briefly review what is known about long-COVID/PASC, its underlying-suspected-pathologies, the pathobiological changes induced by TBI, in other words, the TBI endophenotypes, discuss the intersection of long-COVID/PASC and TBI-induced pathobiologies, and how by considering some of the known factors affecting the person's biological background and the inclusion of mechanistic molecular biomarkers can help to improve the clinical management of TBI patients.

Autoimmunity and long COVID in children

Numerous hypotheses regarding the pathogenetic mechanisms of long COVID have been proposed. Immune dysregulation and autoimmunity are among the leading hypotheses. In this article, we present two clinical cases of long COVID. The first case demonstrates the phenotype of long COVID with pain and musculoskeletal symptoms, which is often associated with autoimmunity and mimics systemic connective tissue diseases. In the second case, a high titer of antinuclear antibodies was observed after SARS-CoV-2 infection, but the clinical symptoms were limited to fever and headache. Only a comprehensive evaluation of clinical symptoms and thorough objective examination can confirm or exclude autoimmune diseases after a previous SARS-CoV-2 infection. A systematic search in the PubMed Medline database was carried out for studies focusing on immune dysregulation, autoimmunity, and its association with the clinical phenotype of long COVID. The question of the role of autoimmunity in the development of long COVID and the management approaches are discussed.

T4 apoptosis in the acute phase of SARS-CoV-2 infection predicts long COVID

Background

As about 10% of patients with COVID-19 present sequelae, it is important to better understand the physiopathology of so-called long COVID.

Method

To this aim, we recruited 29 patients hospitalized for SARS-CoV-2 infection and, by Luminex®, quantified 19 soluble factors in their plasma and in the supernatant of their peripheral blood mononuclear cells, including inflammatory and anti-inflammatory cytokines and chemokines, Th1/Th2/Th17 cytokines, and endothelium activation markers. We also measured their T4, T8 and NK differentiation, activation, exhaustion and senescence, T cell apoptosis, and monocyte subpopulations by flow cytometry. We compared these markers between participants who developed long COVID or not one year later.

Results

None of these markers was predictive for sequelae, except programmed T4 cell death. T4 lymphocytes from participants who later presented long COVID were more apoptotic in culture than those of sequelae-free participants at Month 12 (36.9 ± 14.7 vs. 24.2 ± 9.0%, p = 0.016).

Conclusions

Our observation raises the hypothesis that T4 cell death during the acute phase of SARS-CoV-2 infection might pave the way for long COVID. Mechanistically, T4 lymphopenia might favor phenomena that could cause sequelae, including SARS-CoV-2 persistence, reactivation of other viruses, autoimmunity and immune dysregulation. In this scenario, inhibiting T cell apoptosis, for instance, by caspase inhibitors, could prevent long COVID.